This is an issue since it exists. You have to explicitly call https://www.phpbb.com/customise/db/search
(that's the gear symbol next to the search box in the extension list) and then issue your own username as author (i.e.
) - that way you'll at least find all the posts you wrote.
I even believe in the past UCP > Overview
also contained vertical tabs named "Your extensions" or similar, which also gave you the chance to keep track of which Titania topics had new posts. But I'm not sure anymore, and I suspect nowadays no maintainer would even grasp what I mean.